Treatment of petroleum residua with sodium alloys



United States Patent 3,093,575 TREATMENT OF PETROLEUM RESIDUA WITH SODIUM ALLOYS Charles Newton Kimberlin, Jr., William Judson Mattox, and Clark Edward Adams, all of Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed Nov. 25, 1959, Ser. No. 855,453 Claims. (Cl. 208-208) The present invention relates to a process for upgrading sulfur and metal-containing organic materials, in particular sulfurand metal-containing heavy petroleum fractions, such as residua and reduced crudes.

The problem of sulfur removal from petroleum fractions and crudes is as old as the petroleum industry. For most purposes, it is undesirable to have an appreciable amount of sulfur in any petroleum products. Gasoline should be relatively sulfur-free to make it compatible with lead. Motor fuels containing sulfur as mercaptans are undesirable because of odor and gum formation characteristics. Sulfur is objectionable in fuel oils of any kind because it burns .to form- SO which is obnoxious and corrosive.

Sulfur occurs in petroleum stocks, generally in two main forms, as mercaptans, sulfides, and disulfides, and as part of a more or less substituted ring, of which thiophenes is the prototype. Mercaptans are generally found in the lower boiling fractions, in the naphtha, kerosene, and'light gas oil material. Numerous processes for sulfur removal from relatively low molecular and lower boiling fractions have been suggested such as doctor sweetening, wherein mercaptans are converted to disulfides, caustic treating, solvent extraction, copper chloride treating, etc, all of which give a more or less satisfactory decrease in sulfur or inactivation of mercaptans by their conversion into disulfid'es. The latter remain in the treated product, and must be removed if it is desired to obtain a sulfur-free product.

"Sulphur removal from higher boiling fractions, however, has been a much more difficult operation. Here the sulfur is present for the most part in the less reactive forms as sulfides and as a part of a ring. Such sulfur is, of course, not susceptible to chemical operations satisfactory with mercaptan sulfur. Also, extraction processes are unsatisfactory for solvents specific for sulfur compounds; for instance, boron fluoride complcxes or liquid hydrogen fluoride-boron fluoride, or liquid S 0 no longer are of much use when possibly every molecule of the oil contains a sulfur atom. Thus, a high boiling product, such as a residuum that contains about 3% sulfur is estimated to consist extensively of molecules containing sulfur, and so extraction of sulfur-containing material is no longer feasible inasmuch as the bulk of the material contains sulfur and thus is in the extract and lost unless a means is present for removing sulfur from this extract.

Allied to the sulfur problem in heavy oils and residua is .the problem posed by the presence of heavy metals such as vanadium, nickel, iron and copper in certain crude petroleum oils and residual oils. These metals are particularly undesirable in residual fractions used as fuels due to corrosion and abrasion of construction metals which result from the contact with the hot ash by combustion of these fuels. These metals occur in particular for this service.

s ice in crudes from the Middle East and South America, such as Kuwait and Venezuelan crudes.

Similar to the case of the sulfur compounds referred to above, the metals are also present as a part of a large molecular complex, namely, as the porphyrin molecule. These are highly stable and are not removed by conventional treatments.

It is the principal purpose of the present invention to set forth an improved process for removing sulfur contaminants from high boiling hydrocarbon material, and in particular from residual oils. It is a still further object of the present invention to provide improved means for refining heavy, high boiling petroleum fractions to remove concomitantly sulfur impurities and metal contaminants.

Other and further objects and advantages of the present invention will become more apparent hereinafter.

It has been discovered that these objectives may be achieved and that outstanding sulfur and metals removal are realized when residual fuels are treated with certain molten alloys of sodium, and specifically the alloy of sodium and lead, at elevated temperatures and in the liquid phase. In a preferred embodiment of the invention, an electrolytic process is employed, including a molten lead cathode to synthesize the alloy which is then employed in the residual fuel upgrading.

Sodium metal has often been suggested as a means for removing sulfur from petroleum fractions. However, it has been found that when it is attempted to use this reagent to upgrade residual oils, it is accompanied by several important disadvantages that make it unsuitable In the first place, it is too active under conditions giving acceptable desulfurization, and substantial degrading of the fuel by cracking and carbonization occur. In the second place, it was surprisingly found that the use of the alloy resulted, nonetheless, in a considerably greater selectivity for removing the combined sulfur contained in the molecules of the residual oil than the more active metallic sodium. Consequently the extent of desulfurization obtained by the use of the alloy was considerably higher than resulted from the use of sodium even in highly active emulsified form. In the third place, sodium metal is a considerably more expensive reagent and more hazardous to handle than a sodium alloy.

The alloy may contain from about 2 to 10% sodium, preferably about 6% sodium and the rest being lead or lead in combination with other relatively low melting metals suitable for alloying with sodium, such as tin, cadmium, bismuth, etc., or mixtures of these. In the case of lead alloys, sodium concentrations of about 3 to 6% are preferred since the melting point of the alloy is at a minimum of about 575 to 600 'F., thus permitting lower contacting temperatures in the liquid phase. Alloy containing 10% sodium with lead represents an equiatomic ratio of the two metals and forms a stable compound which does not give as good sulfur removal as the alloy containing less (6%) sodium.

A preferred embodiment of the present invention is shown in the accompanying drawing, which shows in combination a simplified scheme for preparing the alloy electrolytically and thereafter passing the molten alloy to the treating zone for concomitantly removing sulfur and metals from residual fuels.

Turning now to the figure, 2 represents an electrolytic cell for the direct production of sodium in alloy form with lead or mixtures of lead with other metals. This cell consists of one or more carbon anodes in the molten layer of sodium salt. The molten salt layer floats on a layer of molten lead alloy which serves as the cathode. The sodium generated by the electric current is taken up directly by the lead alloy for subsequent use as hereinafter described. A particular advantage for this cell is that it is not necessary to handle metallic sodium, which is a hazardous material, and that the current efiiciency for such a cell is better than that for cells in which metallic sodium is produced in an isolated form. The sodium salt layer is kept in a molten state by the heat generated from the electric current in the cell. The temperature of operation will depend on the composition of the salt layer which may be sodium chloride, recycle sodium sulfide, etc. from the process, or mixtures of sodium salts with or without salts of other metals, such as calcium chloride, which may be used to lower the melting point of the salt mixture. The composition of salts used will be dependent on the particular distribution of the inorganic products desired from the process. For example, if chlorine is desired as a by-product, sodium c1110- ride would be used as the principal sodium salt and chlorine would be liberated at the anode for subsequent recovery. Alternatively, sodium sulfide can be recycled from the process so that sulfur instead of chlorine is liberated and recovered from the cell. In the first case, the cell operation would be similar in part to that for the well known Acker cell described in US. Patent 649,565.

The molten sodium-lead alloy is transferred by pumping or gravity via line 8 and passed to reaction vessel 10, which is a contacting tower, and which may be packed with inert packing, such as chips, Berl saddles or the like.

The petroleum feed may be any fraction from which sulfur is desired to be removed, but the process is particularly adapted to the desulfurization and demetallization of residual fractions which are diificult to treat by other methods; i.e. topped crudes or bottoms from atmospheric or vacuum distillations.

Treating temperatures in tower 10 are in the range of from about 400 to 800 F., preferably 500 to 700 F. For most stocks, temperatures above 700 F. lead to cracking of the residual fuels. The lower temperature limitation is provided by the liquefaction temperature of the alloy so that good contacting is obtained. The pressure within zone 10 is such to insure that substantially all of the oil is maintained in the liquid phase.

Separation from the metal phase is very rapid, so that spent or partially spent alloy, which will contain any unreacted sodium, along with any molten lead and other products are withdrawn downwardly through line 24 and recycled via pump 26 and line 28 to cell 2. The desulfurized oil, however, contains sodium sulfide in suspension, and this is conveniently removed in electrical desalter 16. Desulfurized oil is thus withdrawn from the top of tower 10 through line 12, mixed with a limited amount of water introduced through line 14, sufficient to dissolve the sodium sulfide formed and may amount up to 25% on feed for high sulfur stocks. The mixture is then passed through electrical desalter of conventional design. Desulfurized and demetallized oil is withdrawn through line 18 and passed to tankage, while the sodium sulfide-water solution is withdrawn through line 20 for workup by any known method not forming a part of the present invention, or for return to the electrolytic cell for conversion to sodium as sodium-lead alloy.

The process of the present invention may be modified in many ways obvious to those skilled in the art. Thus the electrolytic cell may be modified in such a manner that the desulfurization actually takes place within the cell. The residual oil is pumped directly into the molten lead-sodium alloy, separated by a bafile from the molten electrolyte, and desulfurized oil product is withdrawn from above the cathode.

4 The advantages derived from operating in accordance with the present invention are illustrated in the following examples.

Example 1 The degree of desulfurization given by various reagents is shown in the table below. The treatments were carried out by contacting a Kuwait vacuum residuum feed with the theoretical amount of sodium to react with the sulfur. The residuum contained 5.2 weight percent sulfur, and the sodium alloys contained 6% to 10% sodium on alloy.

These data demonstrate clearly the superiority of the 6% sodium-lead alloy as a desulfurization agent. They demonstrate that the lead alloy not only has desulfurization properties superior to that of unalloyed sodium, but also superior to other alloys, such as tin.

Example 2 The superior metals removal properties of the leadsodium alloy is shown in the data below. Here an oil containing 90 parts per million of metal as vanadium was treated at 600 F. for 1 hour with equivalent quantities of sodium and the sodium alloys previously described in conjunction with desulfurization.

Percent V removal 6% Na-Pb 88 Na-Pb-Sn 41 Na-Sn 62 Na emulsion 69 The process of the present invention may be subject to many variations. The ratio of sodium to lead in the alloy may range from 2 to 10 wt. percent. The byproducts of the reaction, such as sodium sulfide, may be converted and upgraded by known means, such as hydrolysis, to sodium hydroxide, which is advantageously recycled to cell 2 to provide a low melting point electrolyte. Furthermore, the invention is not limited to the specific electrolytic cell described.

What is claimed is:

1. The process of upgrading a petroleum residual stock which comprises contacting said stock in the liquid phase at a temperature of about 400 to 800 F. with an alloy comprising sodium and lead, said sodium content being at least 2% and less than 10% based on total weight of alloy.

2. The process of claim 1 wherein said alloy is an alloy of lead and sodium, containing about 6% by weight of sodium.

3. An improved process for desulfurizing a sulfur-containing residum which comprises passing into a desulfurization zone a sulfur-containing petroleum residual oil, passing into said zone an alloy of sodium and lead containing about 3 to 6% by weight of sodium based on total weight of alloy, maintaining in said zone a temperature of about 500 to 700 F. and sufiicient pressure to maintain the bulk of the oil in the liquid phase, withdrawing an oil substantially depleted in sulfur, removing sodium sulfide from said oil, and recovering high yields of desulfurized oil.

4. An improved process for desulfurizing a sulfur-containing residual oil which comprises maintaining a layer of a molten sodium salt over a molten lead cathode in an electrolytic cell zone, forming a molten sodium-lead alloy consisting of about 3 to 6% sodium based on total Weight of alloy, passing said molten alloy to a desulfurization zone, passing a sulfur containing petroleum residuum to said zone, maintaining in said zone a temperature of about 500 to 700 F. and sufiicient pressure to maintain the bulk of the oil in the liquid phase, withdrawing oil from said zone, adding water to said Withdrawn stream, passing said stream to an electrical desalting zone, and recovering a residual oil of substantially reduced sulfur content.

5. An improved process for demetallizin g a metal-contaminated residual oil which comprises contacting said oil References Cited in the file of this patent UNITED STATES PATENTS 1,801,412 Carli-sle Apr. 21, 1931 1,859,028 Cross May 17, 1932 1,920,248 Day Aug. 1, 1933 2,058,131 Carlisle Oct. 20, 1936 2,772,211 Hawkes et a l. Nov. 27, 1956 2,927,074 Barger et al. Mar. 1, 1960 

1. THE PROCESS OF UPGRADING A PETROLEUM RESIDUAL STOCK WHICH COMPRISES CONTACTING SAID STOCK IN THE LIQUID PHASE AT A TEMPERATURE OF ABOUT 400* TO 800*F. WITH AN ALLOY COMPRISING SODIUM AND LEAD, SAID SODIUM CONTENT BEING AT LEAST 2% AND LESS THAN 10% BASED ON TOTAL WEIGHT OF ALLOY. 